Abstract
BackgroundNon-essential facultative endosymbionts can provide their hosts with protection from parasites, pathogens, and predators. For example, two facultative bacterial symbionts of the pea aphid (Acyrthosiphon pisum), Serratia symbiotica and Hamiltonella defensa, protect their hosts from parasitism by two species of parasitoid wasp. Previous studies have not explored whether facultative symbionts also play a defensive role against predation in this system. We tested whether feeding on aphids harboring different facultative symbionts affected the fitness of an aphid predator, the lady beetle Hippodamia convergens.ResultsWhile these aphid faculative symbionts did not deter lady beetle feeding, they did decrease survival of lady beetle larvae. Lady beetle larvae fed a diet of aphids with facultative symbionts had significantly reduced survival from egg hatching to pupation and therefore had reduced survival to adult emergence. Additionally, lady beetle adults fed aphids with facultative symbionts were significantly heavier than those fed facultative symbiont-free aphids, though development time was not significantly different.ConclusionsAphids reproduce clonally and are often found in large groups. Thus, aphid symbionts, by reducing the fitness of the aphid predator H. convergens, may indirectly defend their hosts’ clonal descendants against predation. These findings highlight the often far-reaching effects that symbionts can have in ecological systems.
Highlights
Non-essential facultative endosymbionts can provide their hosts with protection from parasites, pathogens, and predators
Lady beetle larvae fed 5AR aphids were 2.56 times more likely to die before pupation than those fed 5AO aphids (p < 0.0127, Figure 1A)
Paederus beetle larvae are protected from wolf spider predation by a polyketide toxin pederin, which is produced by its bacterial symbiont [26,31,32]
Summary
Non-essential facultative endosymbionts can provide their hosts with protection from parasites, pathogens, and predators. Two facultative bacterial symbionts of the pea aphid (Acyrthosiphon pisum), Serratia symbiotica and Hamiltonella defensa, protect their hosts from parasitism by two species of parasitoid wasp. Though some microbial symbionts are parasitic and have detrimental fitness effects for their hosts, many symbionts provide their hosts with fitness benefits [5,6,7] These mutualistic symbionts are generally vertically transmitted from parent to offspring and can be either essential to host survival (obligate, primary) or facultative (secondary) [8,9]. While facultative symbionts are not necessary for survival, they can provide diverse benefits to their hosts, including protection from pathogenic microbes, parasites, and predators [11,12,13,14]. The facultative symbiont Regiella insecticola increases host resistance against several fungal pathogens [18,19]
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